Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare and highly aggressive carcinoma of the skin with a high recurrence rate and propensity for metastasis. It was first described in 1972 and subsequently reclassified as a neuroendocrine tumor. Merkel cells are now thought to arise from the epidermal stem cells, not neural crest progenitor cells, as originally thought, and are the only cutaneous cells that form electron-dense neurosecretory granules. Although rare, the incidence of MCC is rapidly increasing. MCC is more often than not associated with Merkel cell polyomavirus, which may be involved in the malignant transformation and pathogenesis of MCC. Mortality exceeds that of the more commonly occurring skin cancer melanoma, with an overall 5-year survival rate ranging from 30 to 64%. Large reviews have documented recurrence rates ranging from 25 to 50% for local recurrence, 52 to 59% for regional recurrence, and 34 to 36% for distant metastases. Early-stage disease can sometimes be cured with surgery and radiation. Due to the rarity of MCC, statistically significant prospective data are lacking to validate prognostic features and treatment. Therefore, recommendations are largely based on small studies, meta-analyses, and expert consensus. Moreover, no consistent molecular activator in MCC has been identified, resulting in large variability in targeted therapies used in its treatment. New therapies to treat advanced MCC, including immunotherapy, hold promise for improved outcomes in the future. This review summarizes current knowledge regarding the etiology, prognosis, and management of MCC. This review contains 6 figures, 4 tables and 52 references  Key words: Merkel cell carcinoma, Merkel cell polyomavirus, Merkel cell tactile receptor